IVeafheriiiff  of  Clai/  Snh.wils. 
113 
present  the  vast  resources  of  the  subsoil  in  tlie  way  of  the 
mineral  constituents  of  plant  food.  Just  as  by  better  utilisation 
of  the  power  of  leguminous  crops  to  fix  nitrogen,  the  farm 
could  be  rendered  independent  of  any  extraneous  source  of 
this  fertiliser,  so  if  the  phosphoric  acid  and  potash  locked  up 
in  the  subsoil  could  be  rendered  available  for  the  plant,  then 
the  increased  supply  of  mineral  manure,  which  is  the  necessary 
supplement  to  the  extra  nitrogen,  could  also  be  obtained  without 
going  off  the  farm.  As  the  ordinary  })Qor  clay  subsoil  with 
which  Mr.  Mason  was  dealing  contains  in  the  slice  lying 
between  nine  and  eighteen  inches  deep,  no  less  than  one  to 
two  thousand  pounds'  of  phosphoric  acid  and  from  ten  to 
twenty  thousand  pounds  of  potash,  and  as  a big  farm  crop 
would  only  require -40  lb.  and  1,50  lb.  respectively,  there  is 
clearly  plenty  of  scope  for  the  development  of  these  unused 
resources. 
Mr,  Mason’s  scheme  to  unlock  these  reserves  depended 
on  stirring  up  the  subsoil  and  introducing  air  by  means  of 
deep  ploughing  so  that  the  dormant  compounds  of  phosphoric 
acid  and  ])otash  would  pass  over  into  such  a state  of  chemical 
comhination  as  would  be  available  to  the  plant.  The  first  step 
was  to  ascertain  how  the  action  of  the  atmosphere  and  the  natural 
weathering  influences  would  affect  the  composition  of  the  soil. 
Accordingly,  quantities  of  the  clay  subsoil  between  the  depths 
of  nine  and  eighteen  inches  were  dug  out,  dried,  and  powdered. 
Some  portions  were  analysed  in  their  unaltered  condition  and 
the  remainder  was  spread  out  in  shallow  trays  and  placed 
below  a glass  screen  so  that  they  were  protected  from  rain,  but 
otherwise  freely  exposed  to  the  action  of  the  air.'  There  the 
subsoil  was  allowed  to  “ weather  ” for  varying  intervals  of 
time,  after  which  the  contents  of  the  trays  were  again  analysed. 
The  question  was  whether  the  nitrogen  compounds  of  the 
subsoil  could  be  converted  into  nitrates,  the  form  in  which  the 
ordinary  plant  obtains  nitrogen  from  the  soil.  As  regards  the 
mineral  constituents  would  the  phosphates  or  potash  compounds 
become  more  soluble  ? To  answer  this  latter  (juestion  recourse 
was  had  to  the  analytical  process  which  Dr.  Bernard  Dyer  had 
just  then  been  elaborating,  whereby  the  material  that  a weak 
solution  of  citric  acid  can  dissolve  out  of  the  soil  is  regarded  as 
l)eing  “available”  plant  food,  in  contradistinction  to  the  much 
' Most  of  the  analyses  connected  with  Mr.  Mason’s  experiments  were  made 
in  the  Society’s  Chemical  Laboratory  by  Dr.  Voelcker,  under  special  arrange- 
ments sanctioned  by  the  Chemical  and  Woburn  Committee. 
VOL.  (!.-). 
I 
